I really love reading up on these theories, and they offer so many answers and a broad new understanding to our universe.

Yet string theory is in absolute turmoil right now, and "M" theory has become its replacement.Can anybody describe for the benefit of other's, what M theory is, and how it differs from String theory?As I have no idea The idea is - "Lots of youtube video's and explanations "

M-theory is more general - string theory is a special case of M-theory.

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Lee Smolin wrote an excellent critique of string theory called "The Trouble with Physics".

Apparently M-Theory was formulated to try and help researchers decide which version of string theory was correct (there are about 10^500 possible versions of it). It also posits several extra dimensions of spacetime which we may never be able to confirm.

I am not impressed by String Theory because it is extremely hard to test and in the end may be seen as unfalsifiable (How would one falsify that many versions of the same thing?). I also think that the best ideas in science tend to simplify things and make them easier to understand, not to be bewilderingly complex and complicate things.

Of course, I am not a physicist, so take my word with a grain of salt.

I am not impressed by String Theory because it is extremely hard to test and in the end may be seen as unfalsifiable (How would one falsify that many versions of the same thing?). I also think that the best ideas in science tend to simplify things and make them easier to understand, not to be bewilderingly complex and complicate things.

I am impressed with it. It all stems from a single equation (Euler's formula?) which itself is derived from REVOKING an assumption about the nature of the fundamental particles of the universe. That assumption is that the fundamental particles can be modeled as point particles. This works at our vantage point, but actually CAUSES problems in the quantum world.

They changed the assumption to be a ring. This DRAMATICALLY complicated the maths, but led to something interesing.....

The rings can (and in fact should) have vibrational modes. The number of modes for a string is NOT infinite, but is fixed at a definite number. Oddly enough the number of vibrational modes is THE SAME as the number of fundamental particles known and predicted by the Standard Model. Furthermore, the modes appear to correspond to SPECIFIC particles.

ie:

Mode 1 = photonMode 2 = electron....Mode 24 = (drumrole) THE GRAVITON

Gravitons have not been observed, but are predicted to exist. The Standard Model predicts SOME properties of the Graviton, but not all. String Theory predicts properties that the Standard Model does not. String Theory does indeed make predictions, and is testable. It's just that the theory is rather new, and rather different from normal theories. It's taken a while for people to understand it sufficiently to MAKE predictions. It's like Quantum Theory, right after it was created...a lot of head scratching and trying to get ones head around it.

M-Theory is an extension to String Theory, that is necessary, because it was realized that MOST vibrational modes are OPEN, meaning the string is attached to something. That 'something' is spacetime. However, a few modes are CLOSED. The Graviton is a closed-mode particle. This is important! It leads to a SECOND prediction of String Theory! -- The reason that the gravitational force is so profoundly weak compared to the other forces, is because it is NOT bound to our spacetime.

Gravity might be EXACTLY as strong as the other forces. It just 'leaks' off our spacetime plane. Only gravitons that just happen to travel parallel to our plane produce an effect that we can measure.

The ONLY other closed-mode particle would be a so-called "Sterile Neutrino" which would be a neutrino in every way, except that it also would not be bound to our spacetime. Experiments looking for these are also underway, and initial results indicate THAT THEY EXIST. (This has not been confirmed, one lab found something like a 2% excess of neutrinos, others have denied the results, but the positive results are scientifically sound enough that further experiments were IMMEDIATELY enacted)

THIS CAN BE TESTED. The LHC will try to find the graviton, but other experiments can detect it also. Particularly tests involving very large masses placed very close to each other. In this case, gravity should appear VERY MUCH stronger that it does normally, because the proximity of the masses allows fewer gravitons to escape.

If this is verified, it DIRECTLY implies 1) a multiverse and 2) Dark Matter might (at least in part) be gravitational attraction FROM MATTER IN OTHER UNIVERSES.

And, there doesn't have to be an infinite amount of matter in the universe- its just infinitely divisible. In a sense we're just one big 10 or 11 dimensional shape, depending on which theory is correct. So, the patterns really are never broken. In a sense, there is an infinite amount of matter, because if you imagine the two dimensional being, and it needs food somehow, it could acquire an infinite amount of it by dividing the cross sections of a three dimensional object an infinite number of times. Yet, its not infinite, because its limited to being one 3 dimensional shape... Just as the tenth dimension is being limited to one 10 dimensional shape, which is everything in the universe.

I do like the way they explained it though. I do find it rather intriguing that we can be millions of miles away from our house- and never cross its walls. That also makes it funny that someone I was in an argument with said that they could comprehend the fourth dimension..... lol.

I am not impressed by String Theory because it is extremely hard to test and in the end may be seen as unfalsifiable (How would one falsify that many versions of the same thing?). I also think that the best ideas in science tend to simplify things and make them easier to understand, not to be bewilderingly complex and complicate things.

I am impressed with it. It all stems from a single equation (Euler's formula?) which itself is derived from REVOKING an assumption about the nature of the fundamental particles of the universe. That assumption is that the fundamental particles can be modeled as point particles. This works at our vantage point, but actually CAUSES problems in the quantum world.

They changed the assumption to be a ring. This DRAMATICALLY complicated the maths, but led to something interesing.....

The rings can (and in fact should) have vibrational modes. The number of modes for a string is NOT infinite, but is fixed at a definite number. Oddly enough the number of vibrational modes is THE SAME as the number of fundamental particles known and predicted by the Standard Model. Furthermore, the modes appear to correspond to SPECIFIC particles.

ie:

Mode 1 = photonMode 2 = electron....Mode 24 = (drumrole) THE GRAVITON

Gravitons have not been observed, but are predicted to exist. The Standard Model predicts SOME properties of the Graviton, but not all. String Theory predicts properties that the Standard Model does not. String Theory does indeed make predictions, and is testable. It's just that the theory is rather new, and rather different from normal theories. It's taken a while for people to understand it sufficiently to MAKE predictions. It's like Quantum Theory, right after it was created...a lot of head scratching and trying to get ones head around it.

M-Theory is an extension to String Theory, that is necessary, because it was realized that MOST vibrational modes are OPEN, meaning the string is attached to something. That 'something' is spacetime. However, a few modes are CLOSED. The Graviton is a closed-mode particle. This is important! It leads to a SECOND prediction of String Theory! -- The reason that the gravitational force is so profoundly weak compared to the other forces, is because it is NOT bound to our spacetime.

Gravity might be EXACTLY as strong as the other forces. It just 'leaks' off our spacetime plane. Only gravitons that just happen to travel parallel to our plane produce an effect that we can measure.

The ONLY other closed-mode particle would be a so-called "Sterile Neutrino" which would be a neutrino in every way, except that it also would not be bound to our spacetime. Experiments looking for these are also underway, and initial results indicate THAT THEY EXIST. (This has not been confirmed, one lab found something like a 2% excess of neutrinos, others have denied the results, but the positive results are scientifically sound enough that further experiments were IMMEDIATELY enacted)

THIS CAN BE TESTED. The LHC will try to find the graviton, but other experiments can detect it also. Particularly tests involving very large masses placed very close to each other. In this case, gravity should appear VERY MUCH stronger that it does normally, because the proximity of the masses allows fewer gravitons to escape.

If this is verified, it DIRECTLY implies 1) a multiverse and 2) Dark Matter might (at least in part) be gravitational attraction FROM MATTER IN OTHER UNIVERSES.

Pretty cool, eh?

Haha nice post! That tied a few things up, I never knew that the number of "modes" the vibrations of a string had was directly consistent with the number of fundamental particles known.And is this "proof" thing something to do with the "hadron collider"?

Furthermore, what's the deal with the inclusion of an 11th dimension in most versions of string theory?The 10th dimension is a point, with everything and every possibility of everything in every way inside. There cannot be another "everything" in which a transitional line can be drawn?Is there any logical theorem behind the "11th dimension"?

Yes. The LHC should have sufficient energy to create and detect the Higgs Boson. This particle, it is believed, is responsible for the property of mass in ALL particles, including itself. Mass is related to the graviton, obviously. So, although the graviton itself cannot yet be detected, we might be able to learn about how it functions by studying the thing it interacts with...mass.

Furthermore, what's the deal with the inclusion of an 11th dimension in most versions of string theory?The 10th dimension is a point, with everything and every possibility of everything in every way inside. There cannot be another "everything" in which a transitional line can be drawn?Is there any logical theorem behind the "11th dimension"?

10 dimensions are necessary for String Theory to be self-consistent. However, when they realized that some modes are 'open' and some 'closed', they realized that they needed another dimension to account for this degree of freedom. Hence, 11 dimensions.

10 dimensions are necessary for String Theory to be self-consistent. However, when they realized that some modes are 'open' and some 'closed', they realized that they needed another dimension to account for this degree of freedom. Hence, 11 dimensions.

Ah wow Where about would the open/closed string variable dimension be placed then?We understand that the first dimension is a line between two points, the 2nd is a separate line, or a third point, and the 3rd dimension is a fold between the 2nd and 3rd point, etc.what number is this other dimension?It can't be the 11th dimension can it?Is it in place of the 1st dimension, bunging everything up one?Furthermore, I can't conceive to myself how this variable is indeed another dimension.Is it not dissimilar to time? Time being not a dimension, yet allowing the movement of 3rd dimensional objects in 4th dimensional space?

The rings can (and in fact should) have vibrational modes. The number of modes for a string is NOT infinite, but is fixed at a definite number. Oddly enough the number of vibrational modes is THE SAME as the number of fundamental particles known and predicted by the Standard Model. Furthermore, the modes appear to correspond to SPECIFIC particles.

I feel the need to clarify this point. The vibrational modes are simply standing waves, on a string of a fixed length, the Plank length. As such, there is no limit mathematically, to the frequency of the standing waves. They could go to infinity. However, in practice, in actual reality they do not. This is due to another physical process known as pair-production. At some point, the wave would have sufficient energy to spawn off TWO lesser energy particles, and it does so. Pair-production is a confirmed process in nuclear physics.

So, within the energy band of normal physical processes, the number of standing wave modes is limited. This is what corresponds to the number of elementary particles. In order to exceed this energy band, you need something to prevent pair-production. A hyper-strong gravitational would do this, and is probably related to singularities. ie: pair-production is COMPLETELY suppressed and ALL of the strings (particles) actually superimpose on each other. One string, containing ALL the particles of the black hole.

Oddly enough, one of the vibrational modes immediately above the normal cutoff, actually corresponds to a hypothetical object known as a Magnetic Monopole, complete with many of the predicted properties of said object.

I don't understand why people feel the need to make any decisions or judgements on scientific theories, when they are not familiar with the content of the theory (or worse, when they are not even familiar with the entire field). Guys, really smart and experienced scientists have been working with String Theory for decades. You really think your opinion makes more sense than theirs? If some of them think it's worth working on, then it's worth working on.

If you really want to understand String Theory or LQG or something, you're going to need to do a lot of learning. Otherwise, just enjoy the articles in SciAm and admit that everything you know about it is second hand from someone who actually understands it. I mean crap, I'm trained in physics, and I don't pretend that I understand all the nuances of the various fields out there. If I want an opinion on some aspect of String Theory, I go ask an expert about it.

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When I was a kid, I used to pray every night for a new bike. Then I realised, the Lord doesn't work that way. So I just stole one and asked Him to forgive me. - Emo Philips

I don't understand why people feel the need to make any decisions or judgements on scientific theories, when they are not familiar with the content of the theory (or worse, when they are not even familiar with the entire field). Guys, really smart and experienced scientists have been working with String Theory for decades. You really think your opinion makes more sense than theirs? If some of them think it's worth working on, then it's worth working on.

If you really want to understand String Theory or LQG or something, you're going to need to do a lot of learning. Otherwise, just enjoy the articles in SciAm and admit that everything you know about it is second hand from someone who actually understands it. I mean crap, I'm trained in physics, and I don't pretend that I understand all the nuances of the various fields out there. If I want an opinion on some aspect of String Theory, I go ask an expert about it.

Well maybe Jack posted this in hope that there was somebody on this forum who knew about how the theory's developing?We're not 'making judgements', we're just looking for a better understanding?

I have DVDs and books by Hawking and Michio Kaku which touch on String Theory/M-Theory, so i can learn from their expertise, but there's nothing wrong in discussing it is there?

Discussion and learning is awesome. I'm more commenting on the tendancy many people have to lay judgement on the theories, as if they have any idea what they are talking about. This thread has been pretty good, but there have been a few comments to the effect of "I am not impressed by String Theory..." and the like, which sparked me off. Most of my repressed anger probably comes from theists who come in and start spouting about how IBB theory doesn't make sense to them, therefore it's crap and God exists.Sorry if I came off as stifling!

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When I was a kid, I used to pray every night for a new bike. Then I realised, the Lord doesn't work that way. So I just stole one and asked Him to forgive me. - Emo Philips

I do want to comment on how many scientific discoveries reveal how wonderfully bizarre our universe is.

Many theists and supernaturalists object that if the natural universe is all there is, and that there was no magic, then how boring and disappointing reality is. As if to admit, subconsciously, that their god/spirits/psychic powers are all imaginary, the charge is laid that naturalists lack imagination.

Well, if the universe was just what we could see and expect, then that would be something we'd have to accept - whether something is interesting is no indicator of whether it is real or true. Happily, it's not always so. Quantum physics really drove home just how peculiar our universe is. After all, the strange is just whatever deviates from whatever we're used to. The vast scope of the universe means that there's always going to be things that deviate so much from what we're used to, that so long as we're able to keep investigating and learning, we have no need for folk lore to spice things up.